1. Field of the Invention
The present invention relates generally to an antenna device, and more particularly, to an antenna device used for a mobile communication equipment such as a portable telephone set.
2. Description of the Prior Art
An antenna device superior in characteristics such as gain and reflection lose has been required. In addition, as an antenna device used for a mobile communication equipment, a smaller antenna device than conventional antenna devices is required.
As one example of the conventional antenna devices, an inverted-F antenna is described in "Small Antennas" (Research studies press Ltd., England) by K. Fujimoto, A. Henderson, K. Hirasawa and J. R. James. The inverted-F antenna is illustrated in FIG. 18. In FIG. 18, an inverted-F antenna 71 has a rectangular metal plate 72 functioning as a radiating portion. The metal plate 72 is bent so as to be orthogonal to the metal plate 72 from its one side edge, to form a ground terminal 73. On the other hand, the metal plate 72 is similarly bent from its other side edge, to form a power supplying terminal 74. Since the inverted-F antenna 71 has the foregoing structure, the inverted-F antenna 71 can be mounted on a wiring substrate by inserting the ground terminal and the power supplying terminal into through holes provided on the wiring substrate. Since the gain of the inverted-F antenna 71 is not sufficiently large, however, it is difficult to reduce the size of the metal plate 72. As a result, it is difficult to miniaturize the inverted-F antenna 71.
3. Description of the Related Art
In order to solve the problem of the above described inverted-F antenna 71, a substrate surface mounted type antenna having a dielectric substrate has been proposed in copending U.S. patent application Ser. No. 08/230,857 filed in the U.S. Patent Office, which has not been known to the public yet. One example of the surface mounted type antenna is illustrated in FIG. 4. In addition, a surface mounted type antenna constructed by carrying an antenna switch circuit in addition to the antenna shown in FIG. 4 will be described with reference to FIGS. 5 to 8.
Referring to FIG. 4, a surface mounted type antenna 13 comprises a rectangular parallelepiped dielectric substrate 1 composed of ceramics or synthetic resin. Ground electrodes 2 are formed on both side surfaces on the side of the long sides of the dielectric substrate 1. On the other hand, connecting electrodes 3a, 3b and 3c are formed on both side surfaces on the side of the short sides of the dielectric substrate 1. The antenna device further comprises a metal chassis 4 composed of a metal material such as copper or a copper alloy so as to be combined with the dielectric substrate 1. The metal chassis 4 has a rectangular plate-shaped radiating portion 5 and two fixing portions 6 and 7 constructed by bending the radiating portion 5 downward from both ends on the side of its short sides. A power supplying terminal 8 and a ground terminal 9 are integrally formed in an end of the fixing portion 6. The length in the vertical direction of the fixing portion 6 is made smaller than the length in the vertical direction of the fixing portion 7 by the length in the vertical direction of the power supplying terminal 8 and the ground terminal 9. In addition, the length in the vertical direction of the fixing portion 6 including the power supplying terminal 8 and the ground terminal 9 and the length in the vertical direction of the fixing portion 7 are respectively made larger than the thickness of the dielectric substrate 1.
In the surface mounted type antenna 13 shown in FIG. 4, the dielectric substrate 1 is inserted into the metal chassis 4. The side surfaces on the side of the short sides of the dielectric substrate 1 respectively abut against the inner surfaces of the fixing portions 6 and 7 of the metal chassis 4, while a space 10 is formed between the radiating portion 5 of the metal chassis 4 and the surface of the dielectric substrate 1. The space 10 is formed by the dimensional difference between the respective lengths in the vertical direction of the fixing portion 6 having the power supplying terminal 8 and the ground terminal 9 provided therein and the fixing portion 7 and the thickness of the dielectric substrate 1. The connecting electrode 3a formed on the dielectric substrate 1 and the fixing portion 7 of the metal chassis 4 and the connecting electrodes 3b and 3c formed on the dielectric substrate 1 and the power supplying terminal 8 and the ground terminal 9 of the metal chassis 4 are respectively joined to each other by solder.
Furthermore, the above described surface mounted type antenna 13 is mounted on a main wiring substrate 15. On the main wiring substrate 15, a microstrip line 16 for supplying power to an antenna which is connected to an antenna switch circuit (not shown) serving as an antenna circuit, for example, and a ground electrode 17a which is electrically insulated from the microstrip line 16 are formed. Further, a ground electrode 17b is formed on almost the whole reverse surface of the main wiring substrate 15.
In the case of mounting, the surface mounted type antenna 13 is disposed on the surface of the main wiring substrate 15. The power supplying terminal 8 and the microstrip line 16 are soldered to each other, and the ground electrodes 2 and the ground terminal 9 are soldered to the ground electrode 17a on the surface of the main wiring substrate 15. The surface mounted type antenna 13 is thus surface mounted on the surface of the main wiring substrate 15. Radio waves are transmitted to and received from the radiating portion 5 of the metal chassis 4.
In a surface mounted type antenna 35 having an antenna switch circuit 24 shown in FIGS. 5 and 6, a rectangular plate-shaped dielectric substrate 21 having a multilayer structure composed of ceramics or synthetic resin is used. A transmission input portion TX, a receiving output portion RX, control input portions VC1 and VC2 and a plurality of ground electrodes 22 of the antenna switch circuit 24 are formed as outer electrodes on both side surfaces on the side of the long sides of the dielectric substrate 21, while connecting electrodes 23a to 23c are formed on both side surfaces on the side of the short sides thereof. In addition, a strip line 24a, a capacitor 24b and the like are formed as circuit elements inside the dielectric substrate 21, while a diode 24c, a resistor 24d formed by printing and the like are carried as circuit elements on the surface of the dielectric substrate 21. The circuit elements constitute the antenna switch circuit 24. An antenna output portion 24e of the antenna switch circuit 24 inside the dielectric substrate 21 leads to a side surface of the dielectric substrate 21, and is connected to the connecting electrode 23b formed on the side surface. Further, the circuit elements are electrically connected to each other by a suitable inner electrode or a via hole electrode.
A metal chassis 26 is used in combination with the above described dielectric substrate 21. The metal chassis 26 is composed of a metal material such as copper or a copper alloy. The metal chassis 26 has a rectangular plate-shaped radiating portion 27 and two fixing portions 28 and 29 formed by bending the radiating portion 27 downward from both ends on the side of its short sides. A power supplying terminal 30 and a ground terminal 31 are integrally formed in an and or the fixing portion 28. The length in the vertical direction of the fixing portion 28 is made smaller than the length in the vertical direction of the fixing portion 29 by the length in the vertical direction of the power supplying terminal 30 and the ground terminal 31. In addition, the length in the vertical direction of the fixing portion 28 including the power supplying terminal 30 and the ground terminal 31 and the length in the vertical direction of the fixing portion 29 are respectively made larger than the thickness of the dielectric substrate 21.
In the surface mounted type antenna 35 shown in FIG. 6, the dielectric substrate 21 is inserted into the metal chassis 26 in the case of assembling. The side surfaces on the side of the short sides of the dielectric substrate 21 respectively abut against the inner surfaces of the fixing portions 28 and 29 of the metal chassis 26, while a space 32 is formed between the radiating portion 27 of the metal chassis 26 and the surface of the dielectric substrate 21. The space 32 is formed by the dimensional difference between the respective lengths in the vertical direction of the fixing portion 28 including the power supplying terminal 30 and the ground terminal 31 and the fixing portion 29 and the thickness of the dielectric substrate 21. The connecting electrode 23a formed on the dielectric substrate 21 and the fixing portion 29 of the metal chassis 26 and the connecting electrodes 23b and 23c formed on the dielectric substrate 21 and the power supplying terminal 30 and the ground terminal 31 of the metal chassis 26 are respectively joined to each other by solder.
In FIG. 5, connecting electrodes 37 to 40 and a ground electrode 41a electrically insulated from the connecting electrodes 37 to 40 are formed on the surface of a main wiring substrate 36. A ground electrode 41b is formed on almost the whole reverse surface of the main wiring substrate 36.
The substrate surface mounted type antenna 35 is disposed on the surface of the main wiring substrate 36. The transmission input portion TX, the receiving output portion RX and the control input portions VC1 and VC2 are soldered to the connecting electrodes 37 to 40. In addition, the ground electrodes 22 and the ground terminal 31 are soldered to the ground electrode 41a. The surface mounted type antenna 35 is thus surface mounted on the surface of the main wiring substrate 36. Radio waves are transmitted to and received from the radiating portion 27 of the metal chassis 26.
The construction of the antenna switch circuit 24 has been conventionally known. One example of the antenna switch circuit is illustrated in FIG. 7. FIG. 8 is a block diagram showing the antenna 35 having the antenna switch circuit. Another antenna circuit such as a low-pass filter or a band-pass filter can be carried in addition to the antenna switch circuit 24 shown in FIG. 7.
Also in the above described antennas 13 and 35 shown in FIGS. 4 and 5, experience has shown that the following relationship holds among the gain, the frequency bandwidth and the volume occupied by the antenna, so that the miniaturization of the antenna is contrary to higher gain and wider bands: EQU (gain).times.(frequency bandwidth)=(constant).times.(volume occupied by antenna)
Since in the above described substrate surface mounted type antenna 13 or 35 which has not been known yet, the volume occupied by the antenna is small, therefore, gain and band characteristics are not more satisfactory, an compared with a large-sized antenna. Therefore, it is considered that the gain and band characteristics can be enhanced if the substrate surface mounted type antenna 13 or 35 is increased in size. If the antenna 13 or 35 is increased in size, however, the antenna occupies a large area on the main wiring substrate, whereby the size of the whole mobile communication equipment is forced to be increased.
In order to reduce reflection loss, the impedance of the antenna must be so designed that impedance matching is achieved in the mobile communication equipment. However, the impedance of the conventional inverted-F antenna 71 is determined by the position of the power supplying terminal 74, the distance between the ground terminal 73 and the power supplying terminal 74, and the like. In order to set or finely adjust the impedance, therefore, the shape of the inverted-F antenna 71 itself must be changed, thereby to make it difficult to adjust the impedance.
Also in the substrata surface mounted type antenna 13 or 35, the impedance of the antenna is determined by the position of the power supplying terminal, the distance between the ground terminal and the power supplying terminal, and the like. In order to set or finely adjust the impedance, therefore, the shape of the antenna itself must be similarly changed, thereby to make it difficult to adjust the impedance.
Furthermore, in the surface mounted type antenna 13, the power supplying terminal 8, the ground electrodes 2 and the ground terminal 9 are respectively soldered to electrodes on the main wiring substrate 15, whereby the antenna 13 is surface mounted on the main wiring substrate 15. If the antenna 13 is mounted on the main wiring substrate 15 once, therefore, it is difficult to remove the antenna 13 thereafter. On the other hand, after the antenna 13 is surface mounted on the main wiring substrate 15, the power supplying terminal 8 is connected to the antenna switch circuit through the microstrip line 16. Consequently, the impedance of the antenna 13 itself is added to a transmission output from the antenna switch circuit, thereby to make it impossible to accurately measure the transmission output from the antenna switch circuit.
Also in the surface mounted type antenna 35, the transmission input portion TX, the receiving output portion RX, the control input portions VC1 and VC2, the ground electrode 22 and the ground terminal 31 are respectively soldered to electrodes on the main wiring substrate 36, whereby the antenna 35 is surface mounted on the main wiring substrate 36. After the antenna 35 is mounted on the substrate 36 once, therefore, it is difficult to remove the antenna 35. In addition, after the antenna 35 is surface mounted on the main wiring substrate 36, the power supplying terminal 30 is connected to the antenna output portion 24e of the antenna switch circuit 24. Consequently, the impedance of the antenna 35 itself is added to a transmission output from the antenna switch circuit 24, thereby to make it impossible to accurately measure the transmission output from the antenna switch circuit 24.
In order to accurately measure the transmission output from the antenna switch circuit after the antenna 13 or 35 is mounted on the main wiring substrate, therefore, an electrical or mechanical switch for switching the transmission output to a transmission output measuring terminal is required, resulting in increased costs.